Hypoxic tolerance experiments may be helpful to constrain the oxygen requirement for animal evolution. Based on literature review, available data demonstrate that fishes are more sensitive to hypoxia than crustaceans ...Hypoxic tolerance experiments may be helpful to constrain the oxygen requirement for animal evolution. Based on literature review, available data demonstrate that fishes are more sensitive to hypoxia than crustaceans and echinoderms, which in turn are more sensitive than annelids, whilst mollusks are the least sensitive. Mortalities occur where O_2 concentrations are below 2.0 mg/L, equivalent to saturation with oxygen content about 25% PAL（present atmospheric level）. Therefore, the minimal oxygen requirement for maintaining animal diversity since Cambrian is determined as 25% PAL. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. Geological and geochemical studies suggest a constant increase of the oxygen level and a contraction of anoxic oceans during Ediacaran-Cambrian transition when the world oceans experienced a rapid diversification of metazoan lineages. However, fossil first appearances of animal phyla are obviously asynchronous and episodic, showing a sequence as： basal metazoans〉lophotrochozoans〉ecdysozoans and deuterostomes. According to hitherto known data of fossil record and hypoxic sensitivity of animals, the appearance sequence of different animals is broadly consistent with their hypoxic sensitivity： animals like molluscs and annelids that are less sensitive to hypoxia appeared earlier, while animals like echinoderms and fishes that are more sensitive to hypoxia came later. Therefore, it is very likely that the appearance order of animals is corresponding to the increasing oxygen level and/or the contraction of anoxic oceans during Ediacaran-Cambrian transition.展开更多
ObjectiveThe Xixiang biota is a specially preserved micro oryctocoenose discovered in the Lower Cambrian Kuanchuanpu member of Dengying Formation at Zhangjiagou section of Xixiang County in southern Shaanxi Province. ...ObjectiveThe Xixiang biota is a specially preserved micro oryctocoenose discovered in the Lower Cambrian Kuanchuanpu member of Dengying Formation at Zhangjiagou section of Xixiang County in southern Shaanxi Province. The Kuanchuanpu member is a set of neritic carbonate sedimentary formation containing phosphorus and silicon. Its lithology is mainly grey massive fine crystalline, dense massive phosphoruscontaining biolithite and flaggy microcrystallinecrystalline dolomitic limestone. It is in a conformable contact with the underlying upper dolomite member of Dengying Formation and a parallel unconformable contact with the overlying Guojiaba Formation. The fossil assemblages of the Xixiang biota could be compared with the microfbssils from the Lower Cambrian Meishucun Stage, and their age is the Early Cambrian Meishucun Stage.展开更多
New studies suggest that the Kaili Biota in southwestern China's Guizhou Province could be the third revealing evidence for the spectacular Cambrian Explosion of life about 530 million years ago, next to the Burge...New studies suggest that the Kaili Biota in southwestern China's Guizhou Province could be the third revealing evidence for the spectacular Cambrian Explosion of life about 530 million years ago, next to the Burgess Shale Biota of Canada, found in 1909,and the Chengjiang Biota, brought to light in Yunnan Province, China,in 1984.展开更多
The Cambrian Explosion is real Fossil evidence from Chengjiang reveals an assemblage of the fauna, which is represented by at least 100 species. They belong to animal phyla that are still extant, including sponges, cn...The Cambrian Explosion is real Fossil evidence from Chengjiang reveals an assemblage of the fauna, which is represented by at least 100 species. They belong to animal phyla that are still extant, including sponges, cnidarians, ctenophorans, priapulids, annelids(?), arthropods,brachiopods, phoronids, echinoderms and chordates. There are even a number of animal body plans at phylum or subphylum level that are extinct, including: medusiform Eldonia, Facivermis, Tardipolyda, chanccelariids, Dinomischus, hyoliths, Vetuliculid,展开更多
The Cambrian explosion has long been a basic research frontier that concerns many scientific fields. Here we discuss the cause-effect links of the Cambrian explosion on the basis of first appearances of animal phyla i...The Cambrian explosion has long been a basic research frontier that concerns many scientific fields. Here we discuss the cause-effect links of the Cambrian explosion on the basis of first appearances of animal phyla in the fossil record, divergence time, environmental changes, Gene Regulatory Networks, and ecological feedbacks. The first appearances of phyla in the fos- sil record are obviously diachronous but relatively abrupt, concentrated in the first three stages of the Cambrian period （541- 514 Ma）. The actual divergence time may be deep or shallow. Since the gene regulatory networks （GRNs） that control the de- velopment of metazoans were in place before the divergence, the establishment of GRNs is necessary but insufficient for the Cambrian explosion. Thus the Cambrian explosion required environmental triggers. Nutrient availability, oxygenation, and change of seawater composition were potential environmental triggers. The nutrient input, e.g., the phosphorus enrichment in the environment, would cause excess primary production, but it is not directly linked with diversity or disparity. Further in- crease of oxygen level and change of seawater composition during the Ediacaran-Cambrian transition were probably crucial environmental factors that caused the Cambrian explosion, but more detailed geochemical data are required. Many researchers prefer that the Cambrian explosion is an ecological phenomenon, that is, the unprecedented ecological success of ruetazoans during the Early Cambrian, but ecological effects need diverse and abundant animals. Therefore, the establishment of the eco- logical complexity among animals, and between animals and environments, is a consequence rather than a cause of the Cam- brian explosion. It is no doubt that positive ecological feedbacks could facilitate the increase of biodiversity. In a word, the Cambrian explosion happened when environmental changes crossed critical thresholds, led to the initial formation of the meta- zoan-doruinated ecosystem through a series of knock-on ecological processes, i.e., ＂ecological snowball＂ effects.展开更多
The Cambrian explosion was coined to describe the geologically sudden appearance of numerous bilaterian body plans(Phyla)around the Ediacaran-Cambrian transition,around 565-520million years ago.Many explanations and c...The Cambrian explosion was coined to describe the geologically sudden appearance of numerous bilaterian body plans(Phyla)around the Ediacaran-Cambrian transition,around 565-520million years ago.Many explanations and conjectures have been postulated in order to explain the pattern and duration of this explosive radiation of many different phyla of early metazoans.Here,we focus on the evolution of a phylum of marine suspension-feeding animals—the brachiopods,as exemplified by the exceptionally preserved taxa from the celebrated Chengjiang Konservat Lagerst(a|¨)tte(Yunnan,China).The abundant soft-bodied preservation at these fossil quarries gives us the only firm insights into what brachiopods looked like and how they functioned and lived when they first appeared on the Earth.Studies of Chengjiang brachiopods demonstrate that the early animals developed a remarkably varied organization of tissues and organs shortly after the onset of Cambrian explosion.In the marine suspension-feeding brachiopods,most importantly the tentaculate feeding structure of early brachiopods is already differentiated into two shapes of lophophore,anteriorly coiled(spiralled)and posteriorly arching tentacle crowns and the unique latter type was previously not documented from fossil and living brachiopods.Also unlike any known Recent brachiopod,all the known Cambrian brachiopods from Chengjiang have an open digestive tract that was disposed either as a Ushaped gut in linguliform and stem group brachiopods,or straight gut with a posterior anus in some calcareous-shelled stocks.Moreover,in contrast toliving lingulids,all the Cambrian brachiopods have an epibenthic lifestyle either cemented by a ventral valve or attached by variable pedicles to establish complex ecological community encompassing primary tierers and variable secondary tierers.It is therefore assumed that brachiopods were the first benthic metazoan that achieved their success in ecological stratification and tiering complexity by late Atdabanian.The setae are also important for the brachiopod suspension-feeding life style,and in the Chengjiang braehiopods they include two types cilia-like and spine-like setae.The mantle canals of different braehiopod species are also distinctly variable in arrangement,mainly disposed in pinnate,baeulate and peripheral conditions.Of these,the peripheral disposition of mantle canals is for the first time proposed here so as to differentiate from the bifurcate condition in recent lingulids in that the former is devoid of posteriorly extending main trunks of sinus,but possesses a diverging dorsal vascula media in dichotomy.展开更多
The second half of the Ediacaran period began with a large impact - the Acraman impact in South Australia, which was accompanied by a negative δ^13Ccarb anomaly and an extinction-radiation event involving acritarchs....The second half of the Ediacaran period began with a large impact - the Acraman impact in South Australia, which was accompanied by a negative δ^13Ccarb anomaly and an extinction-radiation event involving acritarchs. A few million years later （-570 Ma？） there was a second, deeper and longer-lived world-wide δ^13Ccarb anomaly （the Shuram anomaly） which coincides with extinction of the acanthomorphic acritarchs. Wide distribution of the Shuram event is exemplified by stratigraphic sections from South Australia, Oman, southern California and South China. The widespread anomaly has been tentatively attributed to a marine impact. During recovery from the Shuram event the enigmatic Ediacaran biota achieved its zenith, only to be extirpated and replaced by a polyphyletic assemblage of shelly animals in what is known as the Cambrian ＂explosion＂. This extinction-radiation cycle was preceded by glaciation, another δ^13Ccarb excursion and the highest ^87Sr/^86Sr values known from marine carbonates. These high Sr ratios have been linked to weathering of extensive tracts of continental crust that were elevated during amalgamation of the supercontinent Gondwana. Introduction of essential nutrients to the oceans would have promoted biological production of oxygen and provided P and Ca for the important skeletonization that characterizes the Cambrian ＂explosion＂ and caused a quantum leap in the preservation potential of animal remains. Turbulent events of the last 50 million years of Precambrian time include three glaciations, two large impacts and a massive orogenic episode. These dramatic environmental upheavals are held responsible for three consecutive extinction-radiation cycles that culminated in the appearance of a diverse array of shelly fossils. Various lines of evidence suggest that the metazoans have deep roots so that they too may have been subjected to the environmental pressures of the late Ediacaran period clearly illustrated by acritarchs and the Ediacaran biota but the long-lived diversity of the metazoan population was ＂suddenly＂ revealed by the acquisition of biomineralization.展开更多
The Guanshan Biota from the Cambrian Stage 4 Wulongqing Formation is a typical Burgess-shale type Lagerst？tte that had witnessed the Cambrian explosion. Here we report two new localities of the Guanshan Biota, which ...The Guanshan Biota from the Cambrian Stage 4 Wulongqing Formation is a typical Burgess-shale type Lagerst？tte that had witnessed the Cambrian explosion. Here we report two new localities of the Guanshan Biota, which is located at Baimei village, south of Kunming and Xinglong village, Wuding County, Yunnan Province respectively. Both localities produce soft-body fossils and several new taxa, e.g. a new species of palaeoscolecidans （Palaeoscolex xinglongensis sp. nov.） reported herein. The comparative study of the new species with similar form not only indicates that there is a diversification of palaeoscolecid species in Guanshan Biota, but also strengthens the ties between the older Chengjiang Biota and the younger Kaili Biota （and also the coeval Burgess Shale community）. Three paleoecological features, including high diversity, little disparity and richness of palaeoscolecid worms, are summarized as a case study to represent the differences between Guanshan and Chengjiang Biota.展开更多
Research into the long-recognized‘Cambrian Explosion’of animal life(e.g.,Lipps and Signor,1992;Briggs,2015)has,in recent decades,increasingly sought to resolve the interplay between evolutionary,geochemical and envi...Research into the long-recognized‘Cambrian Explosion’of animal life(e.g.,Lipps and Signor,1992;Briggs,2015)has,in recent decades,increasingly sought to resolve the interplay between evolutionary,geochemical and environmental changes that occurred over an extended Ediacaran to Cambrian transitional interval.This wider interval encompasses several significant geological events,including large-scale glaciations,supercontinental reorganization,global marine transgression,and perturbations in oxygen levels,other isotope proxies,and UV-B radiation(summarised in Narbonne et al.,2012;Meert et al.,2016).These events occurred contemporaneously with evolutionary developments including the radiation of macroscopic eukaryotes,the appearance of the extant animal phyla,the onset of burrowing and biological sediment processing,and the evolution of biomineralization(e.g.,Kouchinsky et al.,2012;Mangano and Buatois,2016;Cunningham et al.,2017).Biological and geological phenomena are widely considered to have been linked during the Ediacaran to Cambrian transition(e.g.,Canfield et al.,2007;Sperling et al.,2013;Boyle et al.,2014;Herringshaw et al.,2017;Shields,2017),and their interaction across this interval is an area of considerable scientific interest.Stratigraphic correlation and subdivision of Ediacaran and Cambrian sections worldwide has been identified as a key objective in order to better understand the co-evolution of the Earth and life systems,and in recent years there have been substantial advances in discussions relating to this challenge(Narbonne et al.,2012;Peng et al.,2012;Landing et al.,2013b;Babcock et al.,2014;Xiao et al.,2016).展开更多
The formation and disruption of supercontinents have significantly impacted mantle dynamics, solid earth processes, surface environments and the biogeochemical cycle. In the early history of the Earth, the collision o...The formation and disruption of supercontinents have significantly impacted mantle dynamics, solid earth processes, surface environments and the biogeochemical cycle. In the early history of the Earth, the collision of parallel intra-oceanic arcs was an important process in building embryonic continents. Superdownwelling along Y-shaped triple junctions might have been one of the important processes that aided in the rapid assembly of continental fragments into closely packed supercontinents. Various models have been proposed for the fragmentation of supercontinents including thermal blanket and superplume hypotheses. The reassembly of supercontinents after breakup and the ocean closure occurs through ＂introversion＂, ＂extroversion＂ or a combination of both, and is characterized by either Pacific-type or Atlantic-type ocean closure. The breakup of supercontinents and development of hydro- thermal system in rifts with granitic basement create anomalous chemical environments enriched in nutri- ents, which serve as the primary building blocks of the skeleton and bone of early modern life forms. A typical example is the rifting of the Rodinia supercontinent, which opened up an N--S oriented sea way along which nutrient enriched upwelling brought about a habitable geochemical environment. The assembly of supercontinents also had significant impact on life evolution. The role played by the Cambrian Gondwana assembly has been emphasized in many models, including the formation of ＇Trans- gondwana Mountains＇ that might have provided an effective source of rich nutrients to the equatorial waters, thus aiding the rapid increase in biodiversity. The planet has witnessed several mass extinction events during its history, mostly connected with major climatic fluctuations including global cooling and warming events, major glaciations, fluctuations in sea level, global anoxia, volcanic eruptions, asteroid impacts and gamma radiation. Some recent models speculate a relationship between superplumes, supercontinent breakup and mass extinction. Upwelling plumes cause continental rifting and formation of large igneous provinces. Subsequent volcanic emissions and resultant plume-induced ＂winter＂ have catastrophic effect on the atmosphere that lead to mass extinctions and long term oceanic anoxia. The assembly and dispersal of continents appear to have influenced the biogeochemical cycle, but whether the individual stages of organic evolution and extinction on the planet are closely linked to Solid Earth processes remains to be investigated.展开更多
Well known for its abundant and extraordinary soft-tissue fossils,the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of ...Well known for its abundant and extraordinary soft-tissue fossils,the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth.The large-scale survey and exploration of the fauna by Chinese paleontologists,partly in collaboration with international scientists,over the past 30 years can be broadly divided into three stages.In the first decade since 1984(19841994),a large number of invertebrates,including basal animals and the protostomes of the early animal tree were discovered,but the subkingdom Deuterostomia was completely unknown.Then in the second decade(19952005),the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals(TPTEA,including basal animals,protostomes and deuterostomes),for the first time.In the third decade(after 2005),the academic community began to think about the internal relationships between the formation of TPTEA and the multiepisode Cambrian explosion,leading to the new hypothesis of the three-episode Cambrian explosion.The Chengjiang fauna is important for deciphering the fauna structure,paleoecological environment,and so on.However,its core academic values mainly rest on two aspects.Firstly,The Chengjiang fauna,as the main phase witness of the Cambrian explosion,has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time.The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion:a step-wise divergent evolution of animals,from basal to highly advanced groups,lasting about 40 million years.In the first phase,it gave birth to a bulk of basal animals(including some now extinct“animal”groups)in the latest Ediacaran,probably including some pioneer protostomes.The second phase took place in the first epoch of the Cambrian period(Terreneuvian),giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals.The third phase proceeded in Cambrian Epoch 2(represented by the Chengjiang fauna),which not only maintained the prosperity of basal animals and protostomes,but also,more importantly,gave birth to all the main phyla of the subkingdom Deuterostomia.Thus,the rudimental framework of the whole TPTEA has been shaped,with the termination of the major innovation events of the Cambrian explosion.Here,we discussed the evolutionary properties of Ediacaran biota,small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups.The order Myllokunmingiida is the only known oldest vertebrate,while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes;Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates;and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes.The second core value of the Chengjiang fauna is of profound humanistic and philosophical significance:the discoveries of the‘first gill openings’,‘first brain’,‘first vertebrae’and‘first heart’provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s“The Descent of Man”.In addition,the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.展开更多
We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parap...We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parapatric, and sympatric speciation. It describes how reproductive isolation of organisms is established through global disasters due to supernova encounters and local disasters due to radioactive volcanic ash fall-outs by continental alkaline volcanism. Our new evolution model uniquely highlights three major factors of disaster-forced speciation： enhanced mutation rate by higher natural radiation level, smaller population size, and shrunken habitat size （i.e., isolation among the individual pop- ulations）. We developed a mathematical model describing speciation of a half-isolated group from a parental group, taking into account the population size （Ne）, immigration rate （m）, and mutation rate （μ）. The model gives a quantitative estimate of the speciation, which is consistent with the observations of speciation speed. For example, the speciation takes at least 105 generations, if mutation rate is less than 10 3 per generation per individual. This result is consistent with the previous studies, in which μ is assumed to be 10 3-10-5. On the other hand, the speciation is much faster （less than l0S generations） for the case that μ is as large as 0.1 in parapatric conditions （m 〈 μ）. Even a sympatric （m ~ 1 ） speciatiou can occur within 103 generations, if mutation rate is very high （μ- 1 mutation per individual per generation）, and if Ne 〈 20-30. Such a high mutation rate is possible during global disasters due to supernova encounters and local disasters due to radioactive ash fall-outs. They raise natural radiation level by a factor of 100-1000. Such rapid speciation events can also contribute to macro-evolution during mass extinction events, such as observed during the Cambrian explosion of biodiversity. A similar rapid speciation （though in a much smaller scale） also has been undergoing in cichlid fishes and great African apes in the last several tens of thousand years in the current African rift valley, including the origin of humankind due to the radioactive ash fall-outs bv continental alkaline volcanism.展开更多
The rapid diversification of early animals during the Ediacaran(635–541 Ma) and early Cambrian(ca.541–509 Ma) has frequently been attributed to increasing oceanic oxygenation. However, the pattern of oceanic oxygena...The rapid diversification of early animals during the Ediacaran(635–541 Ma) and early Cambrian(ca.541–509 Ma) has frequently been attributed to increasing oceanic oxygenation. However, the pattern of oceanic oxygenation and its relationship to early animal evolution remain in debate. In this review,we examine the redox structure of Ediacaran and early Cambrian oceans and its controls, offering new insights into contemporaneous oceanic oxygenation patterns and their role in the coevolution of environments and early animals. We review the development of marine redox models which, in combination with independent distal deep-ocean redox proxies, supports a highly redox-stratified shelf and an anoxia-dominated deep ocean during the Ediacaran and early Cambrian. Geochemical and modeling evidence indicates that the marine redox structure was likely controlled by low atmospheric O2 levels and low seawater vertical mixing rates on shelves at that time. Furthermore, theoretical analysis and increasing geochemical evidence, particularly from South China, show that limited sulfate availability was a primary control on the attenuation of mid-depth euxinia offshore, in contrast to the existing paradigm invoking decreased organic carbon fluxes distally. In light of our review, we infer that if oceanic oxygenation indeed triggered the rise of early animals, it must have done so through a shelf oxygenation which was probably driven by elevated oxidant availability. Our review calls for further studies on EdiacaranCambrian marine redox structure and its controls, particularly from regions outside of South China, in order to better understand the coevolutionary relationship between oceanic redox and early animals.展开更多
Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on th...Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on the temporal and spatial(from shallow to deep waters) variations of the early Cambrian ocean chemistry in South China through analyzing a Fe-S-C systematic dataset integrated from literature.Our investigation indicates that the early Cambrian deep ocean in South China was still anoxic and Fe2+-enriched(i.e.,ferruginous) although its surface was oxic,and in between a metastable euxinic(anoxic and sulfidic) water zone may have dynamically developed in anoxic shelf waters with an increasing weathering sulfate supply.Furthermore,accompanying marine transgression and regression cycles in the early Cambrian,such a "sandwich" structure in ocean redox chemistry demonstrates five evolutional stages,which can be well correlated to the spatiotemporal patterns of fossil records in South China.The good correlation between metazoan fossil occurrences and water chemistry in South China suggests that early animals possibly possessed ability to inhabit anoxic but generally not euxinic environments as free H2S was fatal to most eukaryotes.This view can well explain why those small shell fauna and sponges disappeared from shelf to slope areas where sulfidic Ni-Mo-rich shales were widely deposited.Thus,we conclude that the spatiotemporal variations of ocean chemistry and its biological effects probably played a key role in the phased animal radiations and "extinctions" in the early Cambrian.展开更多
Despite intensive study of the early Cambrian Nanhua Basin(ECNB)in South China,its degree of connectedness to the open ocean remains uncertain,impeding analysis of contemporaneous oceanic redox evolution and its role ...Despite intensive study of the early Cambrian Nanhua Basin(ECNB)in South China,its degree of connectedness to the open ocean remains uncertain,impeding analysis of contemporaneous oceanic redox evolution and its role in the Cambrian Explosion.We analyzed bulk-shale B/Ga,a newly proposed proxy for watermass salinity in ancient depositional systems,for three sections(Daotuo,Yuanjia,and Zhalagou)representing a range of water depths in the ECNB and spanning early Cambrian Stages 2 and 3.The B/Ga proxy records a salinity gradient in the basin,with increasing salinity from shallow-to deep-water areas,particularly during the deposition of black shales of the lower Jiumenchong/Niutitang/Zhalagou Formation.The gradient was probably due to the mixing of freshwater from adjacent landmasses with marine waters within a moderately restricted basin.All three study sections exhibit a monotonic rise in salinity over the~9-Myr study interval,reflecting increased watermass exchange with the open ocean due to regional tectonic and/or global sea-level changes.The improved watermass exchange may have weakened water-column stratification and reduced deep-water anoxia in the ECNB,contributing the enhanced oceanic oxygenation along with global environmental controls and further modulating the expression of the Cambrian Explosion recorded in Lower Cambrian sections of South China.Our study thus highlights the need for comprehensive analyses of hydrographic dynamics in marginal-marine settings that are used to explore co-evolutionary relationships between early animals and environmental oxygen levels.展开更多
基金supported by National Basic Research Program of China (No. 2013CB835002)National Natural Science Foundation of China (No. 41272036)
文摘Hypoxic tolerance experiments may be helpful to constrain the oxygen requirement for animal evolution. Based on literature review, available data demonstrate that fishes are more sensitive to hypoxia than crustaceans and echinoderms, which in turn are more sensitive than annelids, whilst mollusks are the least sensitive. Mortalities occur where O_2 concentrations are below 2.0 mg/L, equivalent to saturation with oxygen content about 25% PAL（present atmospheric level）. Therefore, the minimal oxygen requirement for maintaining animal diversity since Cambrian is determined as 25% PAL. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. Geological and geochemical studies suggest a constant increase of the oxygen level and a contraction of anoxic oceans during Ediacaran-Cambrian transition when the world oceans experienced a rapid diversification of metazoan lineages. However, fossil first appearances of animal phyla are obviously asynchronous and episodic, showing a sequence as： basal metazoans〉lophotrochozoans〉ecdysozoans and deuterostomes. According to hitherto known data of fossil record and hypoxic sensitivity of animals, the appearance sequence of different animals is broadly consistent with their hypoxic sensitivity： animals like molluscs and annelids that are less sensitive to hypoxia appeared earlier, while animals like echinoderms and fishes that are more sensitive to hypoxia came later. Therefore, it is very likely that the appearance order of animals is corresponding to the increasing oxygen level and/or the contraction of anoxic oceans during Ediacaran-Cambrian transition.
基金supported by the National Natural Science Foundation of China (No.41572009)2016 College Students' innovative training program of Chang'an University (grants No.201610710043, 201610710044, 201610710047 and 201610710045)
文摘ObjectiveThe Xixiang biota is a specially preserved micro oryctocoenose discovered in the Lower Cambrian Kuanchuanpu member of Dengying Formation at Zhangjiagou section of Xixiang County in southern Shaanxi Province. The Kuanchuanpu member is a set of neritic carbonate sedimentary formation containing phosphorus and silicon. Its lithology is mainly grey massive fine crystalline, dense massive phosphoruscontaining biolithite and flaggy microcrystallinecrystalline dolomitic limestone. It is in a conformable contact with the underlying upper dolomite member of Dengying Formation and a parallel unconformable contact with the overlying Guojiaba Formation. The fossil assemblages of the Xixiang biota could be compared with the microfbssils from the Lower Cambrian Meishucun Stage, and their age is the Early Cambrian Meishucun Stage.
文摘New studies suggest that the Kaili Biota in southwestern China's Guizhou Province could be the third revealing evidence for the spectacular Cambrian Explosion of life about 530 million years ago, next to the Burgess Shale Biota of Canada, found in 1909,and the Chengjiang Biota, brought to light in Yunnan Province, China,in 1984.
文摘The Cambrian Explosion is real Fossil evidence from Chengjiang reveals an assemblage of the fauna, which is represented by at least 100 species. They belong to animal phyla that are still extant, including sponges, cnidarians, ctenophorans, priapulids, annelids(?), arthropods,brachiopods, phoronids, echinoderms and chordates. There are even a number of animal body plans at phylum or subphylum level that are extinct, including: medusiform Eldonia, Facivermis, Tardipolyda, chanccelariids, Dinomischus, hyoliths, Vetuliculid,
基金supported by National Basic Research Program of China (Grant No. 2013CB835000)National Natural Science Foundation of China (Grant Nos. 40925005, 41272036)+1 种基金the "111 Project" (Grant No. P201102007)the key project from the State Key Laboratory of Continental Dynamics, Northwest University
文摘The Cambrian explosion has long been a basic research frontier that concerns many scientific fields. Here we discuss the cause-effect links of the Cambrian explosion on the basis of first appearances of animal phyla in the fossil record, divergence time, environmental changes, Gene Regulatory Networks, and ecological feedbacks. The first appearances of phyla in the fos- sil record are obviously diachronous but relatively abrupt, concentrated in the first three stages of the Cambrian period （541- 514 Ma）. The actual divergence time may be deep or shallow. Since the gene regulatory networks （GRNs） that control the de- velopment of metazoans were in place before the divergence, the establishment of GRNs is necessary but insufficient for the Cambrian explosion. Thus the Cambrian explosion required environmental triggers. Nutrient availability, oxygenation, and change of seawater composition were potential environmental triggers. The nutrient input, e.g., the phosphorus enrichment in the environment, would cause excess primary production, but it is not directly linked with diversity or disparity. Further in- crease of oxygen level and change of seawater composition during the Ediacaran-Cambrian transition were probably crucial environmental factors that caused the Cambrian explosion, but more detailed geochemical data are required. Many researchers prefer that the Cambrian explosion is an ecological phenomenon, that is, the unprecedented ecological success of ruetazoans during the Early Cambrian, but ecological effects need diverse and abundant animals. Therefore, the establishment of the eco- logical complexity among animals, and between animals and environments, is a consequence rather than a cause of the Cam- brian explosion. It is no doubt that positive ecological feedbacks could facilitate the increase of biodiversity. In a word, the Cambrian explosion happened when environmental changes crossed critical thresholds, led to the initial formation of the meta- zoan-doruinated ecosystem through a series of knock-on ecological processes, i.e., ＂ecological snowball＂ effects.
基金supported by the National Natural Science Foundation of China(4070200541072017+8 种基金40830208)the 973 Project(2013CB835002)111 Project of China(P201102007)Swedish Research Council(VR 2009-43952012-1658 to LEH)ZZF acknowledges grants from the Fok Ying Tung Education Foundationthe China Scholarship Counciland the Ministry of Education of China(FANEDD200936NCET-11-1046)
文摘The Cambrian explosion was coined to describe the geologically sudden appearance of numerous bilaterian body plans(Phyla)around the Ediacaran-Cambrian transition,around 565-520million years ago.Many explanations and conjectures have been postulated in order to explain the pattern and duration of this explosive radiation of many different phyla of early metazoans.Here,we focus on the evolution of a phylum of marine suspension-feeding animals—the brachiopods,as exemplified by the exceptionally preserved taxa from the celebrated Chengjiang Konservat Lagerst(a|¨)tte(Yunnan,China).The abundant soft-bodied preservation at these fossil quarries gives us the only firm insights into what brachiopods looked like and how they functioned and lived when they first appeared on the Earth.Studies of Chengjiang brachiopods demonstrate that the early animals developed a remarkably varied organization of tissues and organs shortly after the onset of Cambrian explosion.In the marine suspension-feeding brachiopods,most importantly the tentaculate feeding structure of early brachiopods is already differentiated into two shapes of lophophore,anteriorly coiled(spiralled)and posteriorly arching tentacle crowns and the unique latter type was previously not documented from fossil and living brachiopods.Also unlike any known Recent brachiopod,all the known Cambrian brachiopods from Chengjiang have an open digestive tract that was disposed either as a Ushaped gut in linguliform and stem group brachiopods,or straight gut with a posterior anus in some calcareous-shelled stocks.Moreover,in contrast toliving lingulids,all the Cambrian brachiopods have an epibenthic lifestyle either cemented by a ventral valve or attached by variable pedicles to establish complex ecological community encompassing primary tierers and variable secondary tierers.It is therefore assumed that brachiopods were the first benthic metazoan that achieved their success in ecological stratification and tiering complexity by late Atdabanian.The setae are also important for the brachiopod suspension-feeding life style,and in the Chengjiang braehiopods they include two types cilia-like and spine-like setae.The mantle canals of different braehiopod species are also distinctly variable in arrangement,mainly disposed in pinnate,baeulate and peripheral conditions.Of these,the peripheral disposition of mantle canals is for the first time proposed here so as to differentiate from the bifurcate condition in recent lingulids in that the former is devoid of posteriorly extending main trunks of sinus,but possesses a diverging dorsal vascula media in dichotomy.
基金the Natural Sciences and Engineering Research Council of Canada for financial assistance in carrying out research on glacial deposits
文摘The second half of the Ediacaran period began with a large impact - the Acraman impact in South Australia, which was accompanied by a negative δ^13Ccarb anomaly and an extinction-radiation event involving acritarchs. A few million years later （-570 Ma？） there was a second, deeper and longer-lived world-wide δ^13Ccarb anomaly （the Shuram anomaly） which coincides with extinction of the acanthomorphic acritarchs. Wide distribution of the Shuram event is exemplified by stratigraphic sections from South Australia, Oman, southern California and South China. The widespread anomaly has been tentatively attributed to a marine impact. During recovery from the Shuram event the enigmatic Ediacaran biota achieved its zenith, only to be extirpated and replaced by a polyphyletic assemblage of shelly animals in what is known as the Cambrian ＂explosion＂. This extinction-radiation cycle was preceded by glaciation, another δ^13Ccarb excursion and the highest ^87Sr/^86Sr values known from marine carbonates. These high Sr ratios have been linked to weathering of extensive tracts of continental crust that were elevated during amalgamation of the supercontinent Gondwana. Introduction of essential nutrients to the oceans would have promoted biological production of oxygen and provided P and Ca for the important skeletonization that characterizes the Cambrian ＂explosion＂ and caused a quantum leap in the preservation potential of animal remains. Turbulent events of the last 50 million years of Precambrian time include three glaciations, two large impacts and a massive orogenic episode. These dramatic environmental upheavals are held responsible for three consecutive extinction-radiation cycles that culminated in the appearance of a diverse array of shelly fossils. Various lines of evidence suggest that the metazoans have deep roots so that they too may have been subjected to the environmental pressures of the late Ediacaran period clearly illustrated by acritarchs and the Ediacaran biota but the long-lived diversity of the metazoan population was ＂suddenly＂ revealed by the acquisition of biomineralization.
基金financially supported by the 973 Project of the Ministry of Science and Technology of China(Grant 2013CB837100)the National Natural Science Foundation of China(Grant 41222014,41172023,41621003,41102012)+4 种基金the National Program for Support of Top-notch Young Professionalsfinancial support from the Ministry of Education of China for Changjiang Scholarthe Program of Introducing Talents of Discipline to Universities(P201102007,W20136100061)Shaanxi Bureau of Science and Technology(FJ11366)Young Talents of Northwest University
文摘The Guanshan Biota from the Cambrian Stage 4 Wulongqing Formation is a typical Burgess-shale type Lagerst？tte that had witnessed the Cambrian explosion. Here we report two new localities of the Guanshan Biota, which is located at Baimei village, south of Kunming and Xinglong village, Wuding County, Yunnan Province respectively. Both localities produce soft-body fossils and several new taxa, e.g. a new species of palaeoscolecidans （Palaeoscolex xinglongensis sp. nov.） reported herein. The comparative study of the new species with similar form not only indicates that there is a diversification of palaeoscolecid species in Guanshan Biota, but also strengthens the ties between the older Chengjiang Biota and the younger Kaili Biota （and also the coeval Burgess Shale community）. Three paleoecological features, including high diversity, little disparity and richness of palaeoscolecid worms, are summarized as a case study to represent the differences between Guanshan and Chengjiang Biota.
文摘Research into the long-recognized‘Cambrian Explosion’of animal life(e.g.,Lipps and Signor,1992;Briggs,2015)has,in recent decades,increasingly sought to resolve the interplay between evolutionary,geochemical and environmental changes that occurred over an extended Ediacaran to Cambrian transitional interval.This wider interval encompasses several significant geological events,including large-scale glaciations,supercontinental reorganization,global marine transgression,and perturbations in oxygen levels,other isotope proxies,and UV-B radiation(summarised in Narbonne et al.,2012;Meert et al.,2016).These events occurred contemporaneously with evolutionary developments including the radiation of macroscopic eukaryotes,the appearance of the extant animal phyla,the onset of burrowing and biological sediment processing,and the evolution of biomineralization(e.g.,Kouchinsky et al.,2012;Mangano and Buatois,2016;Cunningham et al.,2017).Biological and geological phenomena are widely considered to have been linked during the Ediacaran to Cambrian transition(e.g.,Canfield et al.,2007;Sperling et al.,2013;Boyle et al.,2014;Herringshaw et al.,2017;Shields,2017),and their interaction across this interval is an area of considerable scientific interest.Stratigraphic correlation and subdivision of Ediacaran and Cambrian sections worldwide has been identified as a key objective in order to better understand the co-evolution of the Earth and life systems,and in recent years there have been substantial advances in discussions relating to this challenge(Narbonne et al.,2012;Peng et al.,2012;Landing et al.,2013b;Babcock et al.,2014;Xiao et al.,2016).
文摘The formation and disruption of supercontinents have significantly impacted mantle dynamics, solid earth processes, surface environments and the biogeochemical cycle. In the early history of the Earth, the collision of parallel intra-oceanic arcs was an important process in building embryonic continents. Superdownwelling along Y-shaped triple junctions might have been one of the important processes that aided in the rapid assembly of continental fragments into closely packed supercontinents. Various models have been proposed for the fragmentation of supercontinents including thermal blanket and superplume hypotheses. The reassembly of supercontinents after breakup and the ocean closure occurs through ＂introversion＂, ＂extroversion＂ or a combination of both, and is characterized by either Pacific-type or Atlantic-type ocean closure. The breakup of supercontinents and development of hydro- thermal system in rifts with granitic basement create anomalous chemical environments enriched in nutri- ents, which serve as the primary building blocks of the skeleton and bone of early modern life forms. A typical example is the rifting of the Rodinia supercontinent, which opened up an N--S oriented sea way along which nutrient enriched upwelling brought about a habitable geochemical environment. The assembly of supercontinents also had significant impact on life evolution. The role played by the Cambrian Gondwana assembly has been emphasized in many models, including the formation of ＇Trans- gondwana Mountains＇ that might have provided an effective source of rich nutrients to the equatorial waters, thus aiding the rapid increase in biodiversity. The planet has witnessed several mass extinction events during its history, mostly connected with major climatic fluctuations including global cooling and warming events, major glaciations, fluctuations in sea level, global anoxia, volcanic eruptions, asteroid impacts and gamma radiation. Some recent models speculate a relationship between superplumes, supercontinent breakup and mass extinction. Upwelling plumes cause continental rifting and formation of large igneous provinces. Subsequent volcanic emissions and resultant plume-induced ＂winter＂ have catastrophic effect on the atmosphere that lead to mass extinctions and long term oceanic anoxia. The assembly and dispersal of continents appear to have influenced the biogeochemical cycle, but whether the individual stages of organic evolution and extinction on the planet are closely linked to Solid Earth processes remains to be investigated.
基金Natural Science Foundation of China(41672009,41621003,41772010,41720104002)The Strategic Priority Research Program of Chinese Academy of Sciences(XDB18000000,XDB26000000)。
文摘Well known for its abundant and extraordinary soft-tissue fossils,the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth.The large-scale survey and exploration of the fauna by Chinese paleontologists,partly in collaboration with international scientists,over the past 30 years can be broadly divided into three stages.In the first decade since 1984(19841994),a large number of invertebrates,including basal animals and the protostomes of the early animal tree were discovered,but the subkingdom Deuterostomia was completely unknown.Then in the second decade(19952005),the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals(TPTEA,including basal animals,protostomes and deuterostomes),for the first time.In the third decade(after 2005),the academic community began to think about the internal relationships between the formation of TPTEA and the multiepisode Cambrian explosion,leading to the new hypothesis of the three-episode Cambrian explosion.The Chengjiang fauna is important for deciphering the fauna structure,paleoecological environment,and so on.However,its core academic values mainly rest on two aspects.Firstly,The Chengjiang fauna,as the main phase witness of the Cambrian explosion,has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time.The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion:a step-wise divergent evolution of animals,from basal to highly advanced groups,lasting about 40 million years.In the first phase,it gave birth to a bulk of basal animals(including some now extinct“animal”groups)in the latest Ediacaran,probably including some pioneer protostomes.The second phase took place in the first epoch of the Cambrian period(Terreneuvian),giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals.The third phase proceeded in Cambrian Epoch 2(represented by the Chengjiang fauna),which not only maintained the prosperity of basal animals and protostomes,but also,more importantly,gave birth to all the main phyla of the subkingdom Deuterostomia.Thus,the rudimental framework of the whole TPTEA has been shaped,with the termination of the major innovation events of the Cambrian explosion.Here,we discussed the evolutionary properties of Ediacaran biota,small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups.The order Myllokunmingiida is the only known oldest vertebrate,while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes;Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates;and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes.The second core value of the Chengjiang fauna is of profound humanistic and philosophical significance:the discoveries of the‘first gill openings’,‘first brain’,‘first vertebrae’and‘first heart’provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s“The Descent of Man”.In addition,the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.
基金supported by Grants-in-Aid for Scientific Research(23224012) from the Japanese Ministry of Education, Science,Sports,Technology,and Culture
文摘We present the disaster-forced biological evolution model as a general framework that includes Darwinian ＂phylogenic gradualism＂, Eldredge-Gould＇s ＂punctuated equilibrium＂, mass extinctions, and allopatric, parapatric, and sympatric speciation. It describes how reproductive isolation of organisms is established through global disasters due to supernova encounters and local disasters due to radioactive volcanic ash fall-outs by continental alkaline volcanism. Our new evolution model uniquely highlights three major factors of disaster-forced speciation： enhanced mutation rate by higher natural radiation level, smaller population size, and shrunken habitat size （i.e., isolation among the individual pop- ulations）. We developed a mathematical model describing speciation of a half-isolated group from a parental group, taking into account the population size （Ne）, immigration rate （m）, and mutation rate （μ）. The model gives a quantitative estimate of the speciation, which is consistent with the observations of speciation speed. For example, the speciation takes at least 105 generations, if mutation rate is less than 10 3 per generation per individual. This result is consistent with the previous studies, in which μ is assumed to be 10 3-10-5. On the other hand, the speciation is much faster （less than l0S generations） for the case that μ is as large as 0.1 in parapatric conditions （m 〈 μ）. Even a sympatric （m ~ 1 ） speciatiou can occur within 103 generations, if mutation rate is very high （μ- 1 mutation per individual per generation）, and if Ne 〈 20-30. Such a high mutation rate is possible during global disasters due to supernova encounters and local disasters due to radioactive ash fall-outs. They raise natural radiation level by a factor of 100-1000. Such rapid speciation events can also contribute to macro-evolution during mass extinction events, such as observed during the Cambrian explosion of biodiversity. A similar rapid speciation （though in a much smaller scale） also has been undergoing in cichlid fishes and great African apes in the last several tens of thousand years in the current African rift valley, including the origin of humankind due to the radioactive ash fall-outs bv continental alkaline volcanism.
基金supported by the National Natural Science Foundation of China-Research Councils United Kingdom_Natural Environment Research Council Program (41661134048)the National Natural Science Foundation of China (41825019, 41821001), the National Key Research & Development Program of China (2016YFA0601100)+1 种基金111 Project of China (BP0820004) to Chao Li. Meng Chengsupport from the National Natural Science Foundation of China (41703008, 41902027)。
文摘The rapid diversification of early animals during the Ediacaran(635–541 Ma) and early Cambrian(ca.541–509 Ma) has frequently been attributed to increasing oceanic oxygenation. However, the pattern of oceanic oxygenation and its relationship to early animal evolution remain in debate. In this review,we examine the redox structure of Ediacaran and early Cambrian oceans and its controls, offering new insights into contemporaneous oceanic oxygenation patterns and their role in the coevolution of environments and early animals. We review the development of marine redox models which, in combination with independent distal deep-ocean redox proxies, supports a highly redox-stratified shelf and an anoxia-dominated deep ocean during the Ediacaran and early Cambrian. Geochemical and modeling evidence indicates that the marine redox structure was likely controlled by low atmospheric O2 levels and low seawater vertical mixing rates on shelves at that time. Furthermore, theoretical analysis and increasing geochemical evidence, particularly from South China, show that limited sulfate availability was a primary control on the attenuation of mid-depth euxinia offshore, in contrast to the existing paradigm invoking decreased organic carbon fluxes distally. In light of our review, we infer that if oceanic oxygenation indeed triggered the rise of early animals, it must have done so through a shelf oxygenation which was probably driven by elevated oxidant availability. Our review calls for further studies on EdiacaranCambrian marine redox structure and its controls, particularly from regions outside of South China, in order to better understand the coevolutionary relationship between oceanic redox and early animals.
基金financially supported by National Basic Research Program of China(Grant Nos.2013CB955700&2011CB80880)National Natural Science Foundation of China(Grant No.41172030)Program for New Century Excellent Talents in University(Grant No.NCET-11-0724)
文摘Following the Ediacaran metazoan radiation,the "Cambrian Explosion" set up the major framework of todays' animal phyla as well as modern marine ecosystem.Here,we present a preliminary investigation on the temporal and spatial(from shallow to deep waters) variations of the early Cambrian ocean chemistry in South China through analyzing a Fe-S-C systematic dataset integrated from literature.Our investigation indicates that the early Cambrian deep ocean in South China was still anoxic and Fe2+-enriched(i.e.,ferruginous) although its surface was oxic,and in between a metastable euxinic(anoxic and sulfidic) water zone may have dynamically developed in anoxic shelf waters with an increasing weathering sulfate supply.Furthermore,accompanying marine transgression and regression cycles in the early Cambrian,such a "sandwich" structure in ocean redox chemistry demonstrates five evolutional stages,which can be well correlated to the spatiotemporal patterns of fossil records in South China.The good correlation between metazoan fossil occurrences and water chemistry in South China suggests that early animals possibly possessed ability to inhabit anoxic but generally not euxinic environments as free H2S was fatal to most eukaryotes.This view can well explain why those small shell fauna and sponges disappeared from shelf to slope areas where sulfidic Ni-Mo-rich shales were widely deposited.Thus,we conclude that the spatiotemporal variations of ocean chemistry and its biological effects probably played a key role in the phased animal radiations and "extinctions" in the early Cambrian.
基金supported by the Key R&D Project of Ministry of Science and Technology(Grant No.2022YFF0800100)the National Natural Science Foundation of China(Grant Nos.42072335,42002027,41825019,41821001,42130208)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB26000000).
文摘Despite intensive study of the early Cambrian Nanhua Basin(ECNB)in South China,its degree of connectedness to the open ocean remains uncertain,impeding analysis of contemporaneous oceanic redox evolution and its role in the Cambrian Explosion.We analyzed bulk-shale B/Ga,a newly proposed proxy for watermass salinity in ancient depositional systems,for three sections(Daotuo,Yuanjia,and Zhalagou)representing a range of water depths in the ECNB and spanning early Cambrian Stages 2 and 3.The B/Ga proxy records a salinity gradient in the basin,with increasing salinity from shallow-to deep-water areas,particularly during the deposition of black shales of the lower Jiumenchong/Niutitang/Zhalagou Formation.The gradient was probably due to the mixing of freshwater from adjacent landmasses with marine waters within a moderately restricted basin.All three study sections exhibit a monotonic rise in salinity over the~9-Myr study interval,reflecting increased watermass exchange with the open ocean due to regional tectonic and/or global sea-level changes.The improved watermass exchange may have weakened water-column stratification and reduced deep-water anoxia in the ECNB,contributing the enhanced oceanic oxygenation along with global environmental controls and further modulating the expression of the Cambrian Explosion recorded in Lower Cambrian sections of South China.Our study thus highlights the need for comprehensive analyses of hydrographic dynamics in marginal-marine settings that are used to explore co-evolutionary relationships between early animals and environmental oxygen levels.
